An injection molding apparatus has a clamping device which clamps a mold so that a cavity in the mold becomes a closed space, an injection unit which injects a plasticized material into the cavity, and a plasticizing unit which plasticizes the material as basic components.
However, since such conventional injection molding apparatuses are large in size and heavy, they are desired to be compact and light, and various kinds of techniques are proposed. For example, the technique of making a cassette mold compact and light by making the periphery of the cavity a replaceable cassette of an insertion type (see Patent Document 1), and the technique of assembling a screw for plasticizing a material and a motor substantially integrally by a gear meshing structure to make the apparatus compact and light (see Patent Document 2) are proposed.
Techniques of reducing size and weight by providing clamping mechanisms at the injection device side, replacing long screws with short conical screws, and driving the screws by air pressure are proposed (see Patent Documents 3 and 4).    Patent Document 1: Japanese Utility Model Publication No. 7-36729    Patent Document 2: Japanese Patent Application Laid-open No. 11-207744    Patent Document 3: Japanese Patent Application Laid-open No. 8-1740    Patent Document 4: Japanese Patent Publication No. 7-164494